Purified water is a core part of the day-to-day operations of laboratories, with sustainability, and in particular, water usage, emerging as a paramount concern in the field. Here, John Walker, R&D Laboratory Manager, explains how the water footprint of Reverse Osmosis (RO) based processes can be reduced and why systems that claim to be water-saving may not have the impact expected.
Reverse Osmosis based systems are a common solution for generating highly purified water for laboratory applications. RO systems use a semi-permeable membrane to filter impurities from the feed water supply and can be up to 99% efficient. The feed water enters the membrane under pressure and the water molecules pass through, while the contaminants, including particles, dissolved solids, colloids, microorganisms and large biologically-active molecules, will be rejected and discharged to drain.
The nature of the RO process means that a significant amount of wastewater is generated as the concentrate (the water containing the contaminants) is directed to drain. A typical laboratory reverse osmosis (RO) system for purified water may reject 70-90% of the total water processed as waste. In addition, when the RO system starts, to protect subsequent purification technologies, it may automatically reject the water to drain until the permeate produced meets the specifications for the grade of water required. The volume of this initial flush water may typically be around 5 litres; For a system operating at 15% water recovery, this represents less than 1.5% of the water going to drain while generating 60 litres of purified water.
To minimise the volume of water initially rejected to drain, some technologies on the market are designed to direct wastewater back into the feed supply for the same RO until it begins to work as intended. It then reverts to operating as a conventional single pass RO, where all the concentrate water is directed to drain. While this does provide a water saving, it is relatively small compared with the proportion of wastewater produced during normal operation of the RO. Therefore, customers may only see modest reductions in their water footprint.
A more effective approach to reducing water usage is to implement a system that includes multiple RO modules connected in series. This can be achieved with our PURELAB® Chorus 2 + and PURELAB® Chorus 1 Complete. In such a system, the concentrate stream from the first RO is directed into the feed of the second, where further purified water is recovered from what is usually considered a waste product. In effect, this means customers can generate more purified water per litre of feedwater and reduces the volume sent to drain by as much as 50%. To reduce the water footprint further, some systems also employ a third RO module that will process the concentrate from the second.
At Veolia Water Technologies UK (VWT UK), our expert team is able to provide support and guidance on implementing water-saving measures for both new and existing water treatment systems.
Get in touch with our team here to discuss your requirements.
Author | John Walker
R&D Laboratory Manager at ELGA Labwater.
